Semi-quantitative reconstruction of early to late Holocene spring and summer sea ice conditions in the northern Barents Sea

Semi-quantitative estimates of early to late Holocene spring sea ice concentration (SpSIC) and occurrence of summer sea ice for the northern Barents Sea have been obtained by analysing the biomarkers IP25, brassicasterol and a tri-unsaturated highly branched isoprenoid lipid in a Holocene marine sediment core. Sub-surface water mass variations were derived from planktic foraminiferal assemblages and stable isotopes (O-18, C-13). The record indicates paleoceanographic changes over three intervals. During Period I (ca. 9500-5900 cal a BP), the study location experienced the lowest recorded SpSIC (ca. 25%) with short spring seasons and long productive summers, resulting partly from increased Atlantic Water inflow that caused a stronger ocean-atmosphere heat exchange. Throughout Period II (ca. 5900-2700calaBP), the winter sea ice margin migrated southwards and an overall cooling trend resulted in higher SpSIC (ca. 60%) and increased delivery of cold Arctic Water. During Period III (ca. 2700 cal a BP to present), SpSIC increased further (ca. 75%) and some sea ice remained during summer months. A sub-surface warming probably indicates a decoupling of heat exchange between the ocean and the atmosphere. Longer springs and shorter summers were accompanied by the most southerly location of the winter sea ice margin.